This invention relates to the separation of liquids and solids and, more particularly, is concerned with a method of cleaning a filter element of a tube pressure filter which has become "blinded" by solid material, i.e. a large proportion of the pores of the filter element have become blocked by particles of solid material.
Tube pressure filters are a relatively recent addition to the wide range of filtration equipment which can be used for solid-liquid separation. By "tube pressure filter" there is meant herein apparatus which essentially comprises a pair of generally coaxial tubular bodies arranged one within the other and adapted to be supported in a generally upright position, an impermeable elastic sleeve disposed within and secured to the outer tubular body, a filter element disposed around and supported by the inner tubular body, outlet means for the discharge of filtrate which has passed through the filter element and through apertures in the inner tubular body from the interior of the inner tubular body, and means for displacing the tubular bodies axially relative to one another between first and second positions, the arrangement being such that in the first position of said tubular bodies they co-operate with each other to define a closed annular chamber which is divided into generally coaxial and non-intercommunicating inner and outer compartments by said impermeable elastic sleeve, the inner compartment having an inlet for a slurry of a particulate solid material and the outer compartment having an inlet for a hydraulic fluid under pressure, and in the second position of said tubular bodies said annular chamber is open to enable particulate solid material to be discharged from the inner compartment. Details of the construction and operation of tube pressure filters can be found, inter alia, in British Pat. Nos. 1,240,465; 1,240,466; 1,351,131; 1,351,142 and 1,351,943.
As solid particles become lodged in the pores of the filter element of a tube pressure filter during successive filtering cycles and a blinded filter element is formed the permeability of the filter element to filtrate, and thus the filtration rate, are progressively reduced. This has been found to be a major problem when the solid material is a magnesium compound such as magnesium oxide, magnesium hydroxide or magnesium carbonate. When the filtration rate has fallen below an acceptable level it becomes necessary to subject the blinded filter element to a cleaning process to remove at least the major part of the particles lodged in the pores.
An object of the invention is to provide a method of cleaning the filter element of a tube pressure filter which filter element has become blinded with solid material.